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<b>DbEnv::mutex_set_max</b>
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<tt>
<b><pre>
#include &lt;db_cxx.h&gt;
<p>
int
DbEnv::mutex_set_max(u_int32_t max);
<p>
int
DbEnv::mutex_get_max(u_int32_t *maxp);
<p>
int
DbEnv::mutex_set_increment(u_int32_t increment);
<p>
int
DbEnv::mutex_get_increment(u_int32_t *incrementp);
</pre></b>
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<b>Description: DbEnv::mutex_set_max</b>
<p>Configure the total number of mutexes to allocate.</p>
<p>Berkeley DB allocates a default number of mutexes based on the initial
configuration of the database environment.  That default calculation may
be too small if the application has an unusual need for mutexes (for
example, if the application opens an unexpectedly large number of
databases) or too large (if the application is trying to minimize its
memory footprint).  The DbEnv::mutex_set_max method is used to specify an
absolute number of mutexes to allocate.</p>
<p>Calling the DbEnv::mutex_set_max method discards any value previously
set using the DbEnv::mutex_set_increment method.</p>
<p>The database environment's total number of mutexes may also be configured using the
environment's <a href="../ref/env/db_config.html#DB_CONFIG">DB_CONFIG</a> file.  The syntax of the entry in that
file is a single line with the string "mutex_set_max", one or more whitespace
characters, and the total number of mutexes.
Because the <a href="../ref/env/db_config.html#DB_CONFIG">DB_CONFIG</a> file is read when the database environment
is opened, it will silently overrule configuration done before that
time.</p>
<p>The DbEnv::mutex_set_max method configures a database environment, not only operations
performed using the specified <a href="../api_cxx/env_class.html">DbEnv</a> handle.</p>
<p>The DbEnv::mutex_set_max method may not be called after the <a href="../api_cxx/env_open.html">DbEnv::open</a> method is
called.
If the database environment already exists when
<a href="../api_cxx/env_open.html">DbEnv::open</a> is called, the information specified to DbEnv::mutex_set_max
will be ignored.
</p>
<p>The DbEnv::mutex_set_max method
either returns a non-zero error value
or throws an exception that encapsulates a non-zero error value on
failure, and returns 0 on success.
</p>
<b>Parameters</b> <br>
 <b>max</b><ul compact><li>The <b>max</b> parameter is the absolute number of mutexes to
allocate.</ul>
<br>
<br><b>Errors</b>
<p>The DbEnv::mutex_set_max method
may fail and throw
<a href="../api_cxx/except_class.html">DbException</a>,
encapsulating one of the following non-zero errors, or return one of
the following non-zero errors:</p>
<br>
<b>EINVAL</b><ul compact><li>An
invalid flag value or parameter was specified.</ul>
<br>
<hr size=1 noshade>
<b>Description: DbEnv::mutex_get_max</b>
<p>The DbEnv::mutex_get_max method returns the total number of mutexes allocated.</p>
<p>The DbEnv::mutex_get_max method may be called at any time during the life of the
application.</p>
<p>The DbEnv::mutex_get_max method
either returns a non-zero error value
or throws an exception that encapsulates a non-zero error value on
failure, and returns 0 on success.
</p>
<b>Parameters</b> <br>
 <b>maxp</b><ul compact><li>The DbEnv::mutex_get_max method returns  the
total number of mutexes allocated in <b>maxp</b>.</ul>
<br>
<hr size=1 noshade>
<b>Description: DbEnv::mutex_set_increment</b>
<p>Configure the number of additional mutexes to allocate.</p>
<p>Additionally, an application may want to allocate mutexes for its own
use.  The DbEnv::mutex_set_increment method is used to add a number of
mutexes to the default allocation.</p>
<p>Calling the DbEnv::mutex_set_increment method discards any value previously
set using the DbEnv::mutex_set_max method.</p>
<p>The database environment's number of additional mutexes may also be configured using the
environment's <a href="../ref/env/db_config.html#DB_CONFIG">DB_CONFIG</a> file.  The syntax of the entry in that
file is a single line with the string "mutex_set_increment", one or more whitespace
characters, and the number of additional mutexes.
Because the <a href="../ref/env/db_config.html#DB_CONFIG">DB_CONFIG</a> file is read when the database environment
is opened, it will silently overrule configuration done before that
time.</p>
<p>The DbEnv::mutex_set_increment method configures a database environment, not only operations
performed using the specified <a href="../api_cxx/env_class.html">DbEnv</a> handle.</p>
<p>The DbEnv::mutex_set_increment method may not be called after the <a href="../api_cxx/env_open.html">DbEnv::open</a> method is
called.
If the database environment already exists when
<a href="../api_cxx/env_open.html">DbEnv::open</a> is called, the information specified to DbEnv::mutex_set_increment
will be ignored.
</p>
<p>The DbEnv::mutex_set_increment method
either returns a non-zero error value
or throws an exception that encapsulates a non-zero error value on
failure, and returns 0 on success.
</p>
<b>Parameters</b> <br>
 <b>increment</b><ul compact><li>The <b>increment</b> parameter is the number of additional mutexes to
allocate.</ul>
<br>
<br><b>Errors</b>
<p>The DbEnv::mutex_set_increment method
may fail and throw
<a href="../api_cxx/except_class.html">DbException</a>,
encapsulating one of the following non-zero errors, or return one of
the following non-zero errors:</p>
<br>
<b>EINVAL</b><ul compact><li>An
invalid flag value or parameter was specified.</ul>
<br>
<hr size=1 noshade>
<b>Description: DbEnv::mutex_get_increment</b>
<p>The DbEnv::mutex_get_increment method returns the number of additional mutexes to allocate.</p>
<p>The DbEnv::mutex_get_increment method may be called at any time during the life of the
application.</p>
<p>The DbEnv::mutex_get_increment method
either returns a non-zero error value
or throws an exception that encapsulates a non-zero error value on
failure, and returns 0 on success.
</p>
<b>Parameters</b> <br>
 <b>incrementp</b><ul compact><li>The DbEnv::mutex_get_increment method returns  the
number of additional mutexes to allocate in <b>incrementp</b>.</ul>
<br>
<hr size=1 noshade>
<br><b>Class</b>
<a href="../api_cxx/env_class.html">DbEnv</a>
<br><b>See Also</b>
<a href="../api_cxx/env_list.html">Database Environments and Related Methods</a>
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